Project Summary The brain has the remarkable capability to change in response to experience. This plasticity is essential for learning and memory, and is an important feature of the auditory cortex, especially for learning the significance of sensory signals such as speech, for the use of devices such as cochlear implants, and for recovery after short- term deafness. These changes are thought to occur primarily at synapses, basic units of information processing and plasticity. Long-term synaptic plasticity requires sensory experience and activation of neuromodulatory systems which convey behavioral context to local cortical circuits. However, little is known about the interactions between synaptic inputs and release of neuromodulators in vivo, making it challenging to relate perceptual learning to plasticity in the auditory cortex or other brain areas. Recently we developed an approach to measuring dynamics of synaptic modifications for hours, coupled with imaging techniques enabling us to monitor the same cells over days during training, directly monitoring and manipulating activity in behaving mice. These approaches allow for a close examination of links between modulation, cortical plasticity and auditory perceptual learning. Specifically, we will study how auditory perceptual training activates the cholinergic vs noradrenergic modulatory systems. These two modulators are principally involved in selective attention towards behaviorally- important stimuli, general arousal, and learning. However, there may be important functional differences in these systems in terms of when they are active during different phases of training or consequences of cholinergic and noradrenergic modulation on auditory neurons for contextual information processing. This proposal describes a series of imaging, recording, optogenetic, and behavioral experiments that will compare and contrast the effects of locus coeruleus activation and norepinephrine release vs the effects of nucleus basalis activation and cholinergic modulation on the primary auditory cortex of behaving mice. Many studies have highlighted the importance of recording in awake animals during behavior, and we will first examine how ensembles of excitatory and inhibitory neurons are affected by learning over the entire duration of training, as animals go from nave and poor performers, to having reliable performance on an auditory detection and recognition task we have used in the lab for years. Next, we determine when and how cholinergic and noradrenergic modulation affect behavioral and neural responses. Finally, we will make some of the first direct measurements of modulatory neuron responses, asking how these systems are activated by task-relevant variables such as sounds linked to reward. In summary, here we use in vivo recording and imaging methods to ask how behavioral training engages and modifies noradrenergic and cholinergic systems, to collectively affect auditory cortical processing and persistently improve auditory perceptual abilities in behaving mice.